Hot melt adhesives are recognized as adhesives which are tacky when applied in a molten or "hot melt" state. These hot melt adhesives, including pressure sensitive, hot melt adhesives, are typically solids and often tacky at room temperature.
Hot melt adhesives are generally supplied to customers in rigid form for adding to glue pots or other hot melt adhesive processing equipment for melting prior to application. Hot melt adhesives, particularly pressure sensitive adhesives, are also generally supplied to customers at room temperature at which they are extremely tacky. The adhesive properties of pressure sensitive, hot melt adhesives have produced problems in preparation, packaging and processing. For example, pressure sensitive, hot melt adhesives have adhered to other pressure sensitive, hot melt adhesives during packaging, shipping, and storage. Further, hot melt adhesives have adhered to packaging materials such as plastic films, papers or cardboard cartons in various processing conditions.
Attempts have been made to package hot melt adhesives in rigid block portions surrounded by films or other packaging which must be removed prior to supplying the adhesive to a melting pot or other processing equipment. For example, methods and apparatus for packaging hot melt adhesives have been attempted utilizing polymer films filled with molten hot melt adhesive. The high temperature of the molten adhesive has caused melting of certain films including polymer films.
Various of these packaging films have been utilized with certain cooling methods such as water sprays or baths applied to the film during and immediately after filling with the molten, hot melt adhesive. Such packaging processes require elaborate and costly steps and equipment to cool the film during filling. Examples of such water cooled systems are described in U.S. Pat. Nos. 5,373,682 and 5,401,455 to Hatfield. Other plastic films have been utilized to surround individual adhesive masses for packaging to prevent adhesion of the adhesive with other adhesives or packaging.
Attempts have also been made to coat a hot melt adhesive with an anti-adhesive coating prior to wrapping with a plastic film. One such example is proposed in EPO patent 412,867. Also, a micronized powder has been utilized with a silicone coated polymer film to wrap adhesives as proposed in U.S. Pat. No. 5,392,592 to Bozich.
In attempts which have utilized packaging such as polymer films or silicone paper to surround individual adhesive masses, the packaging must be removed from each adhesive mass prior to introducing the adhesive into the melting pot or processing equipment. These film and other wrappers or packages, once removed, create waste and disposal problems. Some polymer films have been used with melting points lower than the melting temperature of the molten pressure sensitive, hot melt adhesive which are designed to be melted in the glue pot with the hot melt adhesive product. These films also create waste in the glue pot and introduce an additive to the adhesive which can adversely affect the adhesive properties of the adhesive.
All of these individually packaged masses which must be removed from individual packaging prior to the introduction into a glue pot, increase time, costs, including labor costs, and waste during application of the adhesive. Such film or individually packaged adhesives may require repetitive tasks of unwrapping by manual labor.
Other attempts have been made to package adhesives utilizing trays or molds formed of a material having non-stick properties or coated with non-tacky material. The adhesive generally has been shipped and transported in these trays for use by the customer where an operation removes the hot melt adhesive product from the tray prior to introduction into the glue pot. The adhesive has been transported in the trays due to the tackiness of the adhesive. Such trays or molds have also been coated with castor oil or powder held in position with static electricity. Generally these trays are costly and produce waste. Such slow cooled adhesives in molds have then generally been individually packaged in film or other exterior individual packaging prior to shipping. One such mold is proposed in U.S. Pat. No. 4,748,796 to Viel.
There is therefore a need to provide methods and apparatus for preparing individual hot melt adhesive masses, particularly of the pressure sensitive type, for packaging which reduces time and costs, including labor costs and steps, and reduces waste resulting from packaging and later processing with the adhesive. Further, there is a need for a hot melt adhesive product which can be utilized without adding waste or deleterious by-products to the adhesive application process.